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He didn't want to hear that he might be wrong so he ignored what CWS wrote.

OK, so I did read the whole thing. The main thing I gleaned from that post is that he has no idea who posted what. The whole thing is written under the assumption that I am the OP and that I made no qualification requirements for the replies.

Second, Mr. Smith is a DIYer who once replaced his own service. IMO that DOES NOT qualify him to give electrical advice or make judgements about other's work.
Many of the issues he mentions are his own opinions and assumptions based on no real world field experience other than the limited work in his own home.
Pardon me for calling a spade a spade.

I really don't need to justify myself to you Bob, but you insinuating that I may be wrong in a situation like this is laughable at best.

Yes, I am aware that some types of conductors are rated up to 40amps under the 90c column of 310.16. Are you aware that Romex is not alowed to exceed the 60c ampacity column per 334.80? I am aware that the 90c column can be used for derating purposes, but the fact remains that that cables ampacity can not exceed 30 amps, period.

Fully agree. It was the "If there was a short, it would nuke the wire and probably cause a fire." comment I felt was over the top. Especially since you and I both know that fault current is FAR higher than the number on any breaker.

I thought it was pretty obvious I was making a joke. Next time I'll try to remember a smiley face on the end there to help guide readers with my meaning.

But my funny comment was not meant to take anything away from CWS's post. I was not trying to be critical of him in what I wrote, just wanted to lighten this up a bit. All of us seem to be quick to jump to conclusions when it comes to code iinterpretation Remember that codes are localized and the level (good or bad) of enforcement varies from county to county and state to state.

For all I know this whole photo may have been a setup and not an actual installation. It might be meant to test the viewer. Only seeing this focused view; you can not tell what lies out of view in the photo; it is difficult to know everything that would need to be known to grade this 'installation' and all its faults. It could be from a building long abandoned from before the NEC even went into affect adandbout to be torn down. There is just no way to know from the photo alone. Taken on its own and assuming its for a building still in use the photo should give anyone pause for further inspection and be hesitant about its use w/o being inspected and corrected as needed by a licensed electrician.

"When we build let us think we build forever. Let it not be for present delight nor for present use alone. Let it be such work that our descendants will thank us for, and let us think, as we lay stone upon stone, that a time is to come when these stones will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, "See! This our fathers did for us."
John Ruskin (1819 - 1900)

Fully agree. It was the "If there was a short, it would nuke the wire and probably cause a fire." comment I felt was over the top. Especially since you and I both know that fault current is FAR higher than the number on any breaker.

I agree that the fault current is far higher than the breaker, which is exactly why an undersized wire would get nuked, resulting in compromised insulation and possibly causing a fire.

I agree that the fault current is far higher than the breaker, which is exactly why an undersized wire would get nuked, resulting in compromised insulation and possibly causing a fire.

The comment I felt was over the top was.... "I call BS"

My point is fault current due to a dead short is in the range of 10,000A. Even with #10cu, this will trip a 40, 50, even 100A breaker without "nuking" conductor.
Have you never seen a main breaker trip due to a smaller branch circuit dead short? I have, many times.

Comment

Yes, I have seen mains trip from downstream shorts, but they will not always reliably trip. They may trip, they may not. Curve times, The type of OCPD, available current and impedance all play a role. I have seen bad ground connections that caused the breaker to take minutes to trip instead of a fraction of a second. Yes, it might trip a larger breaker without nuking the wire, but it could also melt the insulation or the wire. I have seen both scenarios.

To say the fault current is 10,000 amps is a crude guess at best.

Your probably thinking of the maximum interrupting rating (IR) which is the fault current that the Breaker can safely clear without welding closed or blowing up. (Breakers are usually labeled 5,000 or 10,000 AIR) This is a rating and not the actual short circuit current.

Besides the IR rating of the breaker, the conductors must have a short-circuit current rating that will permit the breaker to clear a fault without extensive damage. (Art 110)
Short circuit current will be considerably less at this point in the circuit because it is downstream from the main breaker. But yes, still a big number.

Note; Cooper says #10 wire (@75c not 60c) will have insulation damage at just 2,458 amps for .05 seconds (Or, 3 cycles clearing time) If it takes longer to clear, the number goes way down.

If the available short-circuit current exceeds what the wire can withstand, then the thermal and magnetic forces can cause the the circuit and grounding conductors to NUKE. I don't know the specs, but its safe to say the available short circuit current downstream of an old 40a breaker would exceed the rating of the #10 wire. And yes, possibly nuke it.